However, there is room for improvement in the ripple of the output voltage and the peak value (peak-to-peak value) of the current (coil current) flowing through the inductance element in the conventional step-up/step-down type DC—DC converter. Electronic devices, especially portable electronic devices, are required to operate at low power supply voltages in order to cut power consumption. A stable output voltage (power supply voltage) with a small ripple is required for the DC—DC converter used as the DC power supply of such an electronic device. Also, a larger peak value of the coil current requires the use of an inductance element with larger rated current (that is, larger size), which also increases switching loss. Therefore, it is necessary to develop technology that can reduce the peak value of the coil current as much as possible.